Krox20 B enhancer directs GFP expression in auditory brainstem and other hindbrain neurons but not in the forebrain. (A) Diagram showing components of auditory brainstem. Examples of GFP expression in (B) ventral cochlear nuclei (VCN), (C) lateral superior olive (LSO) and medial nucleus of the trapezoid body (MNTB) and (E) cerebellum. Absence of GFP expression was evident in (F) hippocampus. All images obtained from sagittal and transverse mouse brain slices. Images were acquired using 5X magnification except for (D) MNTB neurons and (F) hippocampus (63X) with a Zeiss LSM 510 Multiphoton Laser Scanning Microscope equipped with 405 and 488 lasers to visualize nuclei (DAPI) and GFP, respectively. 3D image of hippocampal neurons (F inset) was constructed using Volocity software (Perkin Elmer, USA). Scale bar is at 10 μm. Overlapping 5X images and 63X images were taken and compiled to generate composite images of cerebellum and hippocampus for both green (GFP) and blue (DAPI) channels to illustrate distribution of GFP expression in mouse brain. Image contrast enhancement was applied post acquisition for aesthetic reasons.